UbiA prenyltransferase domain-containing protein 1 (UBIAD1) variant c.695 A > G identified in a multigenerational Japanese family with Schnyder corneal dystrophy

PURPOSE

We aimed to identify pathogenic variations in the UbiA prenyltransferase domain-containing protein 1 (UBIAD1) gene in a Japanese family with Schnyder corneal dystrophy (SCD).

STUDY DESIGN

Clinical study METHODS: Three clinically diagnosed SCD patients from a single pedigree participated. Patients 1 and 2 were 69- and 65-year-old sisters, and patient 3 was the 42-year-old daughter of patient 1. Blood samples from the patients were obtained for genetic analysis. Mutation screening of the two UBIAD1 exons was performed using polymerase chain reaction (PCR)-based DNA sequencing.

RESULTS

All participants were found to be heterozygous for the pathogenic missense variation c.695 A > G (p.Asn232Ser) in exon 2 of UBIAD1.

CONCLUSION

This is the first report on the pathogenic UBIAD1 variation c.695 A > G (p.Asn232Ser) in a Japanese population. SCD is a rare corneal dystrophy, and further research on additional cases will aid in the elucidation of disease mechanisms and development of therapeutic strategies.

Multiple Dietary Vitamin K Forms Are Converted to Tissue Menaquinone-4 in Mice

BACKGROUND

Vitamin K is a term that comprises a family of structurally related quinones, phylloquinone (PK) and the menaquinones (MKn), that share a common naphthoquinone ring but vary in sidechain length (n) and saturation. Dietary PK is a biosynthetic precursor to tissue menaquinone-4 (MK4), but little is known about the absorption and metabolism of dietary MKn.

OBJECTIVE

To characterize the absorption and metabolism of dietary MKn relative to PK.

METHODS

In the 4-week diet study, 10-week-old male and female C57BL/6 mice were pair-fed a vitamin K deficient diet (control) or a diet supplemented with 5.0 μmol/kg total PK, MK4, and/or MK9 (separately and in combination). In the 1-week stable isotope study, 12-week-old mice were pair-fed diets containing 2.2 μmol/kg PK (unlabeled control), 2H7PK, 13C11MK4, 2H7MK7, or 2H7MK9. Vitamin K tissue content was quantified by HPLC and/or LC-MS, and concentrations were compared by sex and diet group using 2-factor ANOVA.

RESULTS

Regardless of the form(s) of vitamin K provided in the diet, tissue MK4 concentrations did not differ across equimolar supplemented groups in the kidney, adipose, reproductive organ, bone, or pancreas in either males or females in the diet study (all P values > 0.05). Isotopic labeling confirmed the naphthoquinone ring of MK4 in tissues originated from the administered dietary PK or MKn. Despite equimolar supplementation, accumulation of the administered dietary form differed across diet groups in small intestinal segments (all P values < 0.002) and the liver (P < 0.001). Female mice had greater total vitamin K than males in every tissue examined (P < 0.05).

CONCLUSIONS

Dietary PK, MK4, MK7, and MK9 all served as precursors to tissue MK4 in mice. This study expands our understanding of vitamin K metabolism and supports a common conversion mechanism of all dietary vitamin K forms to MK4. Further investigation of the metabolism and physiological roles of MK4 that may be independent of classical vitamin K function is warranted.